Microbial risk analysis of produce grown on a sustainable chicken production farming system

Background

Tong Ding, David J. Baumler, Xinyu Diao

Sustainable agriculture encourages the use of organic fertilizers instead of synthesized ones, and poultry manure can be recycled as an economical organic fertilizer and added to soil to supply necessary plant nutrients. However, fruits and vegetables in direct contact with manure-contained soil can easily be contaminated by coliforms and food-borne pathogens such as Salmonella spp., E. coli., and Listeria spp. These human pathogens may lead to serious food-borne outbreaks and infections in individuals with weakened immune systems (e.g. children and pregnant women), thus remaining a concern for sustainable farming using poultry manure.In this study, we identified the presence or absence of coliforms and the above three pathogens in the soil samples collected from a sustainable farming system over five months during 2015 in Minnesota and analyzed the risk of microbial contamination. Overall, this study identified that additional control parameters, such as heat or chemical treatment of chicken manure, should be implemented into this practice of sustainable farming to improve the safety of produce items.

MethodsAbstract

Dr. David J. BaumlerXinyu DiaoMorrine OmoloZachary Metz Holly ReilandJustin WiertzemaGreg Schweser

Pathogens may inhabit the GI tract of chicken, and contaminate produce through fecal route.

0.4 - 0.5 µm

2.0 - 5.0 µm

~ 2 µm

Salmonella (non-typhoid)• Present in the environment, domestic and wild animals • Cause disease in 8 to 72 hrs• Infectious dose: 10 – 10 cells• Widely found in chicken manure

In this study, the microbial risk was analyzed by qualitatively and quantitatively detecting coliforms and three food-borne pathogens in the soil fertilized with chicken manure. Manure was harvested from a meat broiler unit at Mirasol Farm in October 2014, spread to a 3 inch thick layer, and was left in between the elderberry rows throughout winter. In spring 2015 the built-up manure was turned lightly and applied to crops as fertilizer. Starting in May 2015, soil and fresh produce samples were collected from this sustainable farming system until September. Salmonella spp. was detected based on the current FDA Bacteriological Analytical Manual. 3M™ Petrifilm™ Environmental Listeria Plates and E. coli/coliform Count Plates were used for Listeria spp. and E. coli/coliform detection respectively.

Results

References

Sustainable agriculture – "An integrated system of plant and animal production practices having a site-specific application that will last over the long term"

Organic fertilizer – Soil amendment derived from natural sources such as animal by-products that provide nutrients like nitrogen and phosphate. Chicken manure contains the highest amount of nitrogen, phosphorus, and potassium among all animal manures that are applicable as fertilizer.

Microbiological hazard – Microbial contamination caused by pathogens found in the air, water, soil, and animals may lead to foodborne illness outbreak. Bacteria, parasites, andviruses are the common pathogens causing outbreaks.

Figure1. The change of the amount of coliforms detected in soil sample and control over 5 months

Table 2. The amount of coliforms / E.coli quantitatively detected in soil sample, soil control, and chicken manure over five months

Pathogen Illnesses Deaths Cost Salmonella (non-typhoid) 1.2 million/year 450/year $3.6 billion/year Listeria monocytogenes 1,600/year 260/year $2.8 billion/year Escherichia coli O157:H7 73,000/year 60/year $271 million/year

Common symptoms Fever, vomiting, nauesa, diarrhea, and abdominal cramps High-risk population The young, old, pregnant, and immuno-compromised individuals

Discussion

This study detected acceptable coliforms / E. coli levels in soil, spinach, and cantaloupes. No Salmonella spp. were qualitatively detectable in all samples, and Listeria spp. were found in harvested cantaloupes.

Soil sample Soil control Manure

May 3.74 / n.a.* 2.60 / n.a. 5.74 / n.a.June 4.16 / n.a. 3.50 / n.a. 5.74 / n.a.July 3.50 / BDL** 4.62 / BDL 5.74 / n.a.Aug. 4.48 / BDL 4.02 / 1.96 5.74 / n.a.Sept. 3.85 / 1.88 2.82 / BDL 5.74 / n.a.

Average 4.08 / 1.88 4.05 / 1.96 5.74 / n.a.0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

9.00

May June July Aug. Sept.

Colif

orm

log

CFU

/g

Soil control

Soil sample

Month Soil sample Soil control ManureMay n.a. n.a. n.a.June N N n.a.July N Y n.a.Aug. N Y n.a.Sept. N Y n.a.

Month Soil sample Soil control ManureMay N N YJune N N YJuly N N YAug. N N YSept. N N Y

Table 3. The presence of Salmonella spp. qualitatively detected in soil sample, soil control, and chicken manure over five months

Table 4. The presence of Listeria spp. qualitatively detected in soil sample, soil control, and chicken manure over five months

Chicken manure is the natural reservoir of human pathogens, with a microbial concentration up to 10 CFU/g.10

What does the Listeria positive detection result mean in this study?The Petrifilm detects environmental Listeria spp. including Listeria monocytogenes, Listeria innocua, and Listeria welshimeri. Although the Listeria spp. found in samples cannot be further identified, the presence of Listeria spp. provides evidence that the environment is suitable for the occurrence of Listeria monocytogenes. Additionally, this pathogen is a cold-tolerant bacterium that can survive the winter climate. Due to the limitation in sampling, we cannot identify what the source of Listeria spp.contamination was. However, the Listeria positive soil control indicates the fresh produce may be contaminated by factors other than the use of manure-amended farming soil. The sheet composting process utilized on this sustainable chicken production farming system is intended to eliminate the pathogens with cold temperature throughout the winter in Minnesota. Nevertheless, small amounts of bacteria may regrow under preferred conditions even after some composting processes.

What may cause microbial contamination in a farming system? Practices such as soil amendment application, irrigation before harvest, gathering, handling, and processing after harvest are factors that may in�uence the microbial safety of the fresh produce. Climate change, wildlife interference, and geographical location can also affect the safety of food.

What should we do to prevent foodborne illness outbreaks?The FDA Food Safety Modernization Act proposed an application interval of 9 months for the use of untreated soil amendment. The amendment should also be applied in a manner without direct contact with the fresh produce. Additional control parameters such as heat or chemical treatment of chicken manure are recommended to minimize the risk of contamination and improve safety.

Chen, Z., & Jiang, X. (2014). Microbiological safety of chicken litter or chicken litter-based organic fertilizers: a review. Agriculture, 4(1), 1-29.Davitt, J. L. (2014). An Assessment of Broiler Litter Bacterial Diversity using Next Generation DNA Sequencing.J.H. Metcalf, P.A. Moore Jr, A.M. Donoghue, K. Arsi, A. Woo-Ming, P.J. Blore, I. Hanning, S.C. Ricke, D.J. Donoghue, Bacterial Content in Runoff from Simulated Rainfall Applied to Plots Amended with Poultry Litter, International Journal of Poultry Science, 2014, 13, 3, 133Kim J, Shepherd MW, Jr., Jiang X (2009) Evaluating the effect of environmental factors on pathogen regrowth in compost extract. Microb Ecol 58: 498-508.Information on foodborne illness outbreaks and related pathogens can be found at http://www.cdc.gov/Information on Food Safety Modernization Act and related legislation can be found at http://www.fda.gov/

47% Salmonella spp. outbreaks

5

asymptomatic disease-carrier

3

Listeria monocytogenes• Present in the environment• Cause disease in 1 to 7 days• Survive and multiply under refrigeration temperature, 5°C • 1 in 20 are asymptomatic carriers Escherichia coli O157: H7

• Present in the environment, domestic and wild animals• Infectious dose: 10 – 10 cells• Coliforms are indicators of fecal contamination

Acknowledgements

Main Street ProjectUpper Midwest Agricultural Safety and Health Center

Cantaloupe #1 Cantaloupe #2 Spinach0.66 1.86 Coliforms (Log CFU/g) 4.00BDL BDL E. coli (CFU/g) n.a.

N Y Listeria spp. NN N Salmonella spp. N

Figure 2. The presence of coliforms / E. coli, Listeria spp., and Salmonella spp. detected in food samples

* n.a. – not applicable** BDL – below detection limit

Department of Food Science and Nutrition, University of Minnesota Twin Cities, 1334 Eckles Ave | St. Paul, MN 55108

Table 1. Information on the foodborne illness outbreaks, related common symptoms, and high-risk population associated with three common pathogens

* n.a. – not applicable** BDL – below detection limit

* n.a. – not applicable** BDL – below detection limit

(Log CFU/g) (Log CFU/g) (Log CFU/g) Month